And consider this: the young male taxi dancer dancing with someone of beginner or intermediate dance skills is immediately apparent to everyone. A taxi dancer dancing with a good dancer at the milonga... you might not know if they are working or if they are dancing socially with a friend from out of town; at that point it doesn't matter anymore because the mission has been accomplished: you've noticed that their partner can really dance.
It's harder to spot a good dancer when they aren't dancing, or when they are only dancing with partners who are less skilled than they are, so I'd argue that advanced dancers have even more to gain from hiring taxi dancers than the "less desirable" dancers, as you put it. For advanced dancers it's not just a chance to get some tandas from the taxi dancer, it's a chance to present themselves in the best way that they possibly can.